More efficient solution to line truncation in DTAttributedLabel, bug fixes in DTCoreTextLayoutFrame

Bug fixes in DTCoreTextLayoutFrame :
- paragraphRanges was not properly calculated when a string isn't ended with '\n'
- uninitialized variable baseWritingDirection in [DTCoreTextLayoutFrame_buildLinesWithTypesetter] so for a attributed strings without paragraph style (by ex. created with [NSAttributedString initWithString:] ) lines were rendered wrong